A precise axial adjustment mechanism based on 6-PSS type parallel mechanism was designed to realize the stroke adjustment in micrometer sizes and the accuracy adjustment in nanometer sizes for optical elements in a photolithographic objective lens. The amount of the prismatic pairs in the 6-PSS type parallel mechanism was improved into 3 from 6 to decrease the usage number of the actuators and increase the reliability of the axial adjustment mechanism. A fillet thin flexure hinge was designed as the spherical hinge in the 6-PSS parallel mechanism to realize monolithic configuration of the axial adjustment mechanism, by which the alignment process of the optical-mechanical components was simplified and the mechanical accuracy of the mechanism was improved. Based on space vector method, the position relationship between input components and output components of the adjustment mechanism was analyzed and the expression of transmission ratio was derived to provide a basis for determining the primary structural dimension of the axial adjustment mechanism. Verification test results of the axial adjustment mechanism show that the numerical result of the transmission ratio is in good agreement with the experimental one; the adjustment stroke of the axial adjustment mechanism is 74.4 μm and the adjustment accuracy is within 40 nm, which satisfies the operation requirement of the photolithographic objective lens.